Communication systems

ABSTRACT

A transmission method for use in a two-hop wireless communication system is provided. The system includes a source apparatus, a destination apparatus and an intermediate apparatus. The source apparatus is operable to transmit information along two links forming a communication path extending from the source apparatus to the destination apparatus via the intermediate apparatus. The intermediate apparatus is operable to receive information from the source apparatus and to transmit the received information to the destination apparatus. The system has access to a time-frequency format for use in assigning available transmission frequency bandwidth during a discrete transmission interval, said format defining a plurality of transmission windows within such an interval. Each window occupies a different part of that interval and has a frequency bandwidth profile within said available transmission frequency bandwidth over its part of that interval. Furthermore, each said window is assignable for such a transmission interval to said source or intermediate apparatus for use in transmission. The transmission method for use in this system includes employing said format to transmit information along the path as two successive transmission signals, link by link, said signals being transmitted using different transmission windows of a particular such transmission interval.

RELATED APPLICATION

This application claims foreign priority benefits under 35 U.S.C. §119of United Kingdom Application No. GB 0616477.6, filed on Aug. 18, 2006,entitled “Communication Systems”.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application relates to the following applications, each of which isincorporated herein by reference:

-   -   COMMUNICATION SYSTEMS, application Ser. No. 11/840,492, filed        Aug. 17, 2007;    -   COMMUNICATION SYSTEMS, application Ser. No. 11/840,518, filed        Aug. 17, 2007;    -   COMMUNICATION SYSTEMS, application Ser. No. 11/840,546, filed        Aug. 17, 2007;    -   COMMUNICATION SYSTEMS, application Ser. No. 11/840,595, filed        Aug. 17, 2007;    -   COMMUNICATION SYSTEMS, application Ser. No. 11/840,621, filed        Aug. 17, 2007;    -   COMMUNICATION SYSTEMS, application Ser. No. 11/840,644, filed        Aug. 17, 2007;    -   COMMUNICATION SYSTEMS, United Kingdom Application No. GB        0616478.4, filed on Aug. 18, 2006;    -   COMMUNICATION SYSTEMS, United Kingdom Application No. GB        0616475.0, filed on Aug. 18, 2006; and    -   COMMUNICATION SYSTEMS, United Kingdom Application No. GB        0616476.8, filed on Aug. 18, 2006.

TECHNICAL FIELD

This invention relates in general to communication systems, and moreparticularly to a frame structure for a multihop communication system.

OVERVIEW

Currently there exists interest in the use of multihop techniques inpacket based radio and other communication systems, where it ispurported that such techniques will enable both extension in coveragerange and increase in system capacity (throughput).

In a multi-hop communication system, communication signals are sent in acommunication direction along a communication path (C) from a sourceapparatus to a destination apparatus via one or more intermediateapparatuses. FIG. 4 illustrates a single-cell two-hop wirelesscommunication system comprising a base station BS (known in the contextof 3G communication systems as “node-B” NB) a relay node RN (also knownas a relay station RS) and a user equipment UE (also known as mobilestation MS). In the case where signals are being transmitted on thedownlink (DL) from a base station to a destination user equipment (UE)via the relay node (RN), the base station comprises the source station(S) and the user equipment comprises the destination station (D). In thecase where communication signals are being transmitted on the uplink(UL) from a user equipment (UE), via the relay node, to the basestation, the user equipment comprises the source station and the basestation comprises the destination station. The relay node is an exampleof an intermediate apparatus (I) and comprises: a receiver, operable toreceive data from the source apparatus; and a transmitter, operable totransmit this data, or a derivative thereof, to the destinationapparatus.

Simple analogue repeaters or digital repeaters have been used as relaysto improve or provide coverage in dead spots. They can either operate ina different transmission frequency band from the source station toprevent interference between the source transmission and the repeatertransmission, or they can operate at a time when there is notransmission from the source station.

FIGS. 5a and 5b illustrate a number of applications for relay stations.For fixed infrastructure, the coverage provided by a relay station maybe “in-fill” to allow access to the communication network for mobilestations which may otherwise be in the shadow of other objects orotherwise unable to receive a signal of sufficient strength from thebase station despite being within the normal range of the base station.“Range extension” is also shown, in which a relay station allows accesswhen a mobile station is outside the normal data transmission range of abase station. One example of in-fill shown at the top right of FIG. 5bis positioning of a nomadic relay station to allow penetration ofcoverage within a building that could be above, at, or below groundlevel.

Other applications are nomadic relay stations which are brought intoeffect for temporary cover, providing access during events oremergencies/disasters. A final application shown in the bottom right ofFIG. 5a provides access to a network using a relay positioned on avehicle.

Relays may also be used in conjunction with advanced transmissiontechniques to enhance gain of the communications system as explainedbelow.

It is known that the occurrence of propagation loss, or “pathloss”, dueto the scattering or absorption of a radio communication as it travelsthrough space, causes the strength of a signal to diminish. Factorswhich influence the pathloss between a transmitter and a receiverinclude: transmitter antenna height, receiver antenna height, carrierfrequency, clutter type (urban, sub-urban, rural), details of morphologysuch as height, density, separation, terrain type (hilly, flat). Thepathloss L (dB) between a transmitter and a receiver can be modeled by:L=b+10n log d  (A)Where d (meters) is the transmitter-receiver separation, b(db) and n arethe pathloss parameters and the absolute pathloss is given byl=10^((L/10)).

The sum of the absolute path losses experienced over the indirect linkSI+ID may be less than the pathloss experienced over the direct link SD.In other words it is possible for:L(SI)+L(ID)<L(SD)  (B)

Splitting a single transmission link into two shorter transmissionsegments therefore exploits the non-linear relationship between pathlossverses distance. From a simple theoretical analysis of the pathlossusing equation (A), it can be appreciated that a reduction in theoverall pathloss (and therefore an improvement, or gain, in signalstrength and thus data throughput) can be achieved if a signal is sentfrom a source apparatus to a destination apparatus via an intermediateapparatus (e.g. relay node), rather than being sent directly from thesource apparatus to the destination apparatus. If implementedappropriately, multi-hop communication systems can allow for a reductionin the transmit power of transmitters which facilitate wirelesstransmissions, leading to a reduction in interference levels as well asdecreasing exposure to electromagnetic emissions. Alternatively, thereduction in overall pathloss can be exploited to improve the receivedsignal quality at the receiver without an increase in the overallradiated transmission power required to convey the signal.

Multi-hop systems are suitable for use with multi-carrier transmission.In a multi-carrier transmission system, such as FDM (frequency divisionmultiplex), OFDM (orthogonal frequency division multiplex) or DMT(discrete multi-tone), a single data stream is modulated onto N parallelsub-carriers, each sub-carrier signal having its own frequency range.This allows the total bandwidth (i.e. the amount of data to be sent in agiven time interval) to be divided over a plurality of sub-carriersthereby increasing the duration of each data symbol. Since eachsub-carrier has a lower information rate, multi-carrier systems benefitfrom enhanced immunity to channel induced distortion compared withsingle carrier systems. This is made possible by ensuring that thetransmission rate and hence bandwidth of each subcarrier is less thanthe coherence bandwidth of the channel. As a result, the channeldistortion experienced on a signal subcarrier is frequency independentand can hence be corrected by a simple phase and amplitude correctionfactor. Thus the channel distortion correction entity within amulticarrier receiver can be of significantly lower complexity of itscounterpart within a single carrier receiver when the system bandwidthis in excess of the coherence bandwidth of the channel.

Orthogonal frequency division multiplexing (OFDM) is a modulationtechnique that is based on FDM. An OFDM system uses a plurality ofsub-carrier frequencies which are orthogonal in a mathematical sense sothat the sub-carriers' spectra may overlap without interference due tothe fact they are mutually independent. The orthogonality of OFDMsystems removes the need for guard band frequencies and therebyincreases the spectral efficiency of the system. OFDM has been proposedand adopted for many wireless systems. It is currently used inAsymmetric Digital Subscriber Line (ADSL) connections, in some wirelessLAN applications (such as WiFi devices based on the IEEE 802.11a/gstandard), and in wireless MAN applications such as WiMAX (based on theIEEE 802.16 standard). OFDM is often used in conjunction with channelcoding, an error correction technique, to create coded orthogonal FDM orCOFDM. COFDM is now widely used in digital telecommunications systems toimprove the performance of an OFDM based system in a multipathenvironment where variations in the channel distortion can be seenacross both subcarriers in the frequency domain and symbols in the timedomain. The system has found use in video and audio broadcasting, suchas DVB and DAB, as well as certain types of computer networkingtechnology.

In an OFDM system, a block of N modulated parallel data source signalsis mapped to N orthogonal parallel sub-carriers by using an InverseDiscrete or Fast Fourier Transform algorithm (IDFT/IFFT) to form asignal known as an “OFDM symbol” in the time domain at the transmitter.Thus, an “OFDM symbol” is the composite signal of all N sub-carriersignals. An OFDM symbol can be represented mathematically as:

$\begin{matrix}{{{x(t)} = {\frac{1}{\sqrt{N}}{\sum\limits_{n = 0}^{N - 1}{c_{n} \cdot {\mathbb{e}}^{j\; 2\;\pi\; n\;\Delta\; f\; t}}}}},{0 \leq t \leq T_{s}}} & (1)\end{matrix}$where Δf is the sub-carrier separation in Hz, Ts=1/Δf is symbol timeinterval in seconds, and c_(n) are the modulated source signals. Thesub-carrier vector in (1) onto which each of the source signals ismodulated cεC_(n), c=(c₀, c₁ . . . c_(N-1)) is a vector of Nconstellation symbols from a finite constellation. At the receiver, thereceived time-domain signal is transformed back to frequency domain byapplying Discrete Fourier Transform (DFT) or Fast Fourier Transform(FFT) algorithm.

OFDMA (Orthogonal Frequency Division Multiple Access) is a multipleaccess variant of OFDM. It works by assigning a subset of sub-carriers,to an individual user. This allows simultaneous transmission fromseveral users leading to better spectral efficiency. However, there isstill the issue of allowing bi-directional communication, that is, inthe uplink and download directions, without interference.

In order to enable bi-directional communication between two nodes, twowell known different approaches exist for duplexing the two (forward ordownload and reverse or uplink) communication links to overcome thephysical limitation that a device cannot simultaneously transmit andreceive on the same resource medium. The first, frequency divisionduplexing (FDD), involves operating the two links simultaneously but ondifferent frequency bands by subdividing the transmission medium intotwo distinct bands, one for forward link and the other for reverse linkcommunications. The second, time division duplexing (TDD), involvesoperating the two links on the same frequency band, but subdividing theaccess to the medium in time so that only the forward or the reverselink will be utilizing the medium at any one point in time. Bothapproaches (TDD & FDD) have their relative merits and are both well usedtechniques for single hop wired and wireless communication systems. Forexample the IEEE 802.16 standard incorporates both an FDD and TDD mode.As an example, FIG. 6 illustrates the single hop TDD frame structureused in the OFDMA physical layer mode of the IEEE 802.16 standard(WiMAX).

Each frame is divided into DL and UL subframes, each being a discretetransmission interval. They are separated by Transmit/Receive andReceive/Transmit Transition Guard interval (TTG and RTG respectively).Each DL subframe starts with a preamble followed by the Frame ControlHeader (FCH), the DL-MAP, and the UL-MAP.

The FCH contains the DL Frame Prefix (DLFP) to specify the burst profileand the length of the DL-MAP. The DLFP is a data structure transmittedat the beginning of each frame and contains information regarding thecurrent frame; it is mapped to the FCH.

Simultaneous DL allocations can be broadcast, multicast and unicast andthey can also include an allocation for another BS rather than a servingBS. Simultaneous ULs can be data allocations and ranging or bandwidthrequests.

SUMMARY OF EXAMPLE EMBODIMENTS

In accordance with one embodiment of the present invention, atransmission method for use in a two-hop wireless communication systemis provided. The system includes a source apparatus, a destinationapparatus and an intermediate apparatus. The source apparatus isoperable to transmit information along two links forming a communicationpath extending from the source apparatus to the destination apparatusvia the intermediate apparatus. The intermediate apparatus is operableto receive information from the source apparatus and to transmit thereceived information to the destination apparatus. The system has accessto a time-frequency format for use in assigning available transmissionfrequency bandwidth during a discrete transmission interval, said formatdefining a plurality of transmission windows within such an interval.Each window occupies a different part of that interval and has afrequency bandwidth profile within said available transmission frequencybandwidth over its part of that interval. Furthermore, each said windowis assignable for such a transmission interval to said source orintermediate apparatus for use in transmission. The transmission methodfor use in this system includes employing said format to transmitinformation along the path as two successive transmission signals, linkby link, said signals being transmitted using different transmissionwindows of a particular such transmission interval.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and itsadvantages, reference is now made to the following description, taken inconjunction with the accompanying drawings, in which:

FIG. 1 shows a frame structure;

FIG. 2 shows node activity within each zone;

FIG. 3 shows an example of zone usage within one cell;

FIG. 4 shows a single-cell two-hop wireless communication system;

FIGS. 5a and 5b show applications of relay stations; and

FIG. 6 shows a single hop TDD frame structure used in the OFDMA physicallayer mode of the IEEE 802.16 standard.

DETAILED DESCRIPTION

When a node is required to support two independent links to twodifferent nodes, e.g. a relay station communicating with a base stationand a mobile, the existing TDD or FDD frame structures require somemodification in order to make realization of the relay practical.Particular embodiments of the invention provide a frame structure(format) for a multihop communication system that is an extension of thestandard TDD frame structure.

One proposed frame structure is designed for the case that the controlinformation originating from the head node that controls the overallmedium access is receivable by all subordinate nodes operating in thenetwork. It is further designed in a manner that enables legacy singlehop TDD mobile devices that have no knowledge of a relay station tooperate within the new relaying enabled system.

If control information is not receivable from the head node (or sourceapparatus) then an extra frame period is required for two-hoptransmission. This is because control information sent by the sourceapparatus to the intermediate apparatus cannot then be received by thedestination apparatus in the same frame. The destination apparatus(especially a legacy apparatus) will be designed to receive such controlinformation at the beginning of the frame and therefore an extra frameperiod is required for the intermediate apparatus to transmit thecontrol information on to the source at the beginning of the frame (inthe preamble) and then transmit the data. Thus a frame latency of 1 isincurred.

An example frame structure is shown in FIG. 1. It is composed of anumber of transmission and reception zones for both the downlink anduplink sub-frames. The zone types are either:

-   B Broadcast of control related information such as: synchronization    sequences, commands, information and details of the structure or    layout of the frame.-   C Dedicated control information that is transmitted in a    non-broadcast zone (i.e. either to individual or a group of    receivers)-   T Dedicated user-data (transport) transmission    The 9 different zones identified in FIG. 1 are described in Table 1.

TABLE 1 Description of the zones. Zone Number Label Description 1 PPreamble or synchronization sequence transmissions for cellidentification 2 MAP Frame format description (zone boundaries,allocations within the zones, etc) 3 BS-RS/BS- BS to RS transmissionzone. Can also be MS used for BS to MS transmission if spatial divisionmultiple access is supported (i.e. the same transmission resource can beused to communicate with more than one entity) 4 BS-MS BS to MStransmission zone. RS is not active during this period, it is processingany received information and turning around prior to transmission. 5BS-MS/RS- RS to MS transmission zone. Can also be MS used by the BS totransmitted to MSs that do not experience significant levels ofinterference from RS transmissions. 6 MS-BS/MS- MS control informationtransmission zone. RS Information can be received by both the RS and theBS. Control information can be information or requests from the MS. 7MS-BS/MS- MS to RS transmission zone. Can also be RS used by MSs who donot cause interference to the RS to transmit to the BS. 8 MS-BS MS to BStransmission zone. RS is not actively transmitting or receiving duringthis period; it is processing any received information prior to turningaround. 9 RS-BS/MS- RS to BS transmission zone. Can also be BS used forMS to BS transmission if spatial division multiple access is supported(i.e. the same transmission resource can be used to communicate withmore than one entity)

FIG. 2 illustrates a preferred operation of the BS, RS and MS in termsof its activity within each of the zones described in Table 1.

FIG. 3 indicates one particular realization of the proposed framestructure in terms of how different user types may be allocated fortransmission or reception within the various zone types.

In this case there are five link types identified (A-E), as illustratedin FIG. 3. A description of the zones that are used in this example isgiven in Table 2.

TABLE 2 Description of example of zone usage within one cell. DL Zone ULZone Link Usage Usage Comments (A) (1), (2), (5) (6), (7) MS and RS arespatially separated and therefore significant interference isolationexists. User does not support SDMA. (B) (1), (2), (3) (6), (9) MS and RSare spatially separated and therefore significant interference isolationexists. User does support SDMA. (C) (1), (2), (3), (6), (7), (9) RSreceives data in (3) and (7) and (5) then transmits in (5) and (9)thereby enabling in-frame relaying. (D) (1), (2), (5) (6), (7) MScommunicates with BS via RS. Transmission to the RS happens at thebeginning of the UL subframe (7) to allow sufficient RS relay processingtime. (E) (1), (2), (4) (6), (8) MSs that communicate directly with theBS that are not isolated from the RS use zones (4) & (8) to prevent RSinterference from impairing link performance.

One of the advantages of adopting the proposed frame structure ofinvention embodiments is that the BS can make use of all of thetransmission resource all of the time to communicate with the RS and MSnodes in the network. This is enabled by reusing the transmissionresource used on the RS to MS link for BS to MS communications. In orderto effect this, and prevent such a reuse approach from causing excessinterference, the BS must ensure that the users it communicates withinthis reuse zone (i.e. zones (5) & (9)) are sufficiently isolated fromthe users communicating with the RS. Thus, the BS essentially requires amechanism to decide whether the users with which it communicates shouldbe in the reuse zone (i.e. zones (5) & (9)) or the normal zone (i.e.zones (4) & (8)).

There are numerous algorithms that can be used to form such a mechanism.A few examples are listed below:

-   1. Ask the MS to perform a carrier-to-interference-plus-noise (CINR)    measurement on the BS transmission during the reuse zone and during    the normal zone. If the CINR is much higher in the normal zone then    allocate the user to the normal zone. If the CINR is similar, then    allocate the user to the reuse zone.-   2. Start with all users in the normal zone. If the normal zone    becomes fully loaded and cannot accommodate more users without the    risk of imposing a reduction on the quality of service new and    existing users will experience, then identify candidate users to    move from the normal zone to the reuse zone. If subsequently the    reported CINR for a user communicating with the BS in the reuse zone    falls below a particular threshold then move that to the normal    zone.    In summary, benefits of particular embodiments may include:-   Enabling the construction and operation of simple, low cost relays    that do not need to generate any control information or perform    scheduling-   Maximize spectral efficiency by ensuring that the BS does not have    any time in the frame when it is idle-   Minimize latency by enabling two-hop relaying to occur within one    frame-   Enable the system to potentially provide transparent operation to a    legacy single-hop TDD users-   The possibility to further improve spectral efficiency through using    SDMA based techniques to enable the same transmission resource    (frequency & time) to be used between the BS and the RSs and MSs    within a cell.-   Provide a mechanism to enable reuse of the RS-MS communication zone    by the BS to communicate directly with MSs that will not cause a    degradation in RS-MS link performance by performing such    communications.

Embodiments of the present invention may be implemented in hardware, oras software modules running on one or more processors, or on acombination thereof. That is, those skilled in the art will appreciatethat a microprocessor or digital signal processor (DSP) may be used inpractice to implement some or all of the functionality of a transmitterembodying the present invention. The invention may also be embodied asone or more device or apparatus programs (e.g. computer programs andcomputer program products) for carrying out part or all of any of themethods described herein. Such programs embodying the present inventionmay be stored on computer-readable media, or could, for example, be inthe form of one or more signals. Such signals may be data signalsdownloadable from an Internet website, or provided on a carrier signal,or in any other form.

Although the present invention has been described with severalembodiments, a myriad of changes, variations, alterations,transformations, and modifications may be suggested to one skilled inthe art, and it is intended that the present invention encompass suchchanges, variations, alterations, transformations, and modifications asfall within the scope of the appended claims.

What is claimed is:
 1. A transmission method for use in a two-hoptime-division-duplex wireless communication system, the systemcomprising a source apparatus, destination apparatuses and anintermediate apparatus, said source apparatus being configured totransmit information along two links forming an indirect communicationpath extending from the source apparatus to at least one of thedestination apparatuses via the intermediate apparatus, and theintermediate apparatus being configured to receive information from thesource apparatus and to transmit the received information to the atleast one destination apparatus, a time-frequency format for downlinkand uplink subframes used for transmission in the system in discretetransmission periods, each discrete transmission period being a singledownlink or a single uplink subframe with a plurality of transmissionzones within each transmission period, each zone occupying a differentpart of that period, and being assignable to said source or intermediateapparatus for use in transmission, the method comprising: transmittinginformation along the path as two successive transmission signals, linkby link, said signals being transmitted using different zones of aparticular transmission period; wherein: a control information zone inthe particular transmission period is used for broadcast of controlinformation from said source apparatus to said intermediate apparatusand said destination apparatuses; a first zone in the particulartransmission period is used for transmission from said source apparatusto said intermediate apparatus and a second, subsequent zone in theparticular transmission period is used for transmission from saidintermediate apparatus to the at least one destination apparatus; saidfirst and second transmission zones of the transmission period areeither side in time of a third transmission zone of the transmissionperiod, which is used for transmission along a single link forming adirect communication path from said source apparatus to anotherdestination apparatus, and in which there is no transmission orreception by the intermediate apparatus, but processing is performed insaid intermediate apparatus, so as to configure the information fortransmission in the second transmission zone based upon the informationreceived in the first transmission zone; said second zone is also usedfor direct transmission along a single link forming a directcommunication path from said source apparatus to a further destinationapparatus on the downlink; and said control information enables saidintermediate apparatus and said destination apparatuses to receivetransmissions in said first zone and said second zone, the methodfurther comprising: employing said first transmission zone to transmitinformation from the source apparatus to a still further destinationapparatus along a single link forming a direct communication path, sothat information is transmitted from the source apparatus to both saidintermediate apparatus and said still further destination apparatusduring the part of the particular transmission period corresponding tothe first transmission zone; determining whether the destinationapparatuses can receive the control information from the sourceapparatus and adding an extra control information zone in the particulartransmission period for broadcast of control information from saidintermediate apparatus to said destination apparatus based on thedetermination.
 2. The transmission method according to claim 1, whereinsaid control zone occupies a part of the transmission period precedingthe part of the transmission period occupied by the first transmissionzone.
 3. The transmission method according claim 1, comprising:employing said second transmission zone to transmit information from thesource apparatus to the said further destination apparatus along thedirect communication path, so that information is transmitted from saidintermediate apparatus to said destination apparatus and from the sourceapparatus to said further destination apparatus during the part of thetransmission period corresponding to the second transmission zone. 4.The transmission method according to claim 1, comprising: employing saidthird transmission zone to transmit information from another sourceapparatus to said at least one of the destination apparatuses along adirect communication path, so that information is transmitted from thatanother source apparatus during said processing in the intermediateapparatus.
 5. The transmission method according to claim 1, comprising:employing said first transmission zone to transmit information fromanother source apparatus to said at least one of the destinationapparatuses along a direct communication path, so that information istransmitted from the source apparatus to said intermediate apparatus andfrom that another source apparatus to said at least one of thedestination apparatuses during the part of the transmission periodcorresponding to the first transmission zone.
 6. The transmission methodaccording claim 1, comprising: employing said second transmission zoneto transmit information from another source apparatus to said at leastone of the destination apparatuses along the direct communication path,so that information is transmitted from said intermediate apparatus tosaid at least one of the destination apparatuses and from that anothersource apparatus to said at least one of the destination apparatusesduring the part of the transmission period corresponding to the secondtransmission zone.
 7. The transmission method according to claim 1,comprising employing a space division multiple access technique in oneor more of said transmission zones of the transmission period.
 8. Thetransmission method according to claim 1, wherein said system is an OFDMor OFDMA system, and wherein the time-frequency format is a format foran OFDM or OFDMA downlink or uplink sub-frame of an OFDM or OFDMAtime-division-duplex frame.
 9. The transmission method according toclaim 1, wherein each said discrete transmission period is a sub-frameperiod.
 10. The transmission method according to claim 1, wherein eachsaid transmission zone comprises a zone in an OFDM or OFDMA framestructure.
 11. The transmission method according to claim 1, wherein theor each source apparatus is a base station.
 12. The transmission methodaccording to claim 1, wherein the or each source apparatus is a userterminal.
 13. The transmission method according to claim 1, wherein theor each destination apparatus is a base station.
 14. The transmissionmethod according to claim 1, wherein the or each destination apparatusis a user terminal.
 15. The transmission method according to claim 1,wherein the or each intermediate apparatus is a relay station.
 16. Atwo-hop wireless time-division-duplex communication system, the systemcomprising: a source apparatus, destination apparatuses and anintermediate apparatus, said source apparatus being configured totransmit information along two links forming an indirect communicationpath extending from the source apparatus to at least one of thedestination apparatus via the intermediate apparatus, and theintermediate apparatus being configured to receive information from thesource apparatus and to transmit the received information to the atleast one destination apparatus; the system using a time-frequencyformat for downlink and uplink subframes for transmission in the systemin discrete transmission periods, each discrete transmission periodbeing a single downlink or a single uplink subframe with a plurality oftransmission zones within each transmission period, each zone occupyinga different part of that period and being assignable to said source orintermediate apparatus for use in transmission; and further comprising atransmitter configured to employ said format to transmit informationalong the relayed path as two successive transmission signals, link bylink, using transmission zones of a particular transmission period,wherein a control information zone in the particular transmission periodis used for broadcast of control information from said source apparatusto said intermediate apparatus and said destination apparatuses; a firstzone in the particular transmission period is used for transmission fromsaid source apparatus to said intermediate apparatus and a second,subsequent zone in the particular transmission period is used fortransmission from said intermediate apparatus to the at least onedestination apparatus; said first and second transmission zones of thetransmission period are either side in time of a third transmission zoneof the transmission period, which is used for transmission along asingle link forming a direct communication path from said sourceapparatus to a further destination apparatus, and in which there is notransmission or reception by the intermediate apparatus, but processingis performed in said intermediate apparatus, so as to configure theinformation for transmission in the second transmission zone based uponthe information received in the first transmission zone; said secondzone is also used for direct transmission along a single link forming adirect communication path from said source apparatus to a furtherdestination apparatus on the downlink; and said control informationenables said intermediate apparatus and said destination apparatuses toreceive transmissions in said first zone and said second zone; andwherein said first transmission zone is used to transmit informationfrom the source apparatus to a still further destination apparatus alonga single link forming a direct communication path, so that informationis transmitted from the source apparatus to both said intermediateapparatus and said still further destination apparatus during the partof the particular transmission period corresponding to the firsttransmission zone; wherein the system further comprises a processor thatdetermines whether the destination apparatuses can receive the controlinformation from the source apparatus and adding an extra controlinformation zone in the particular transmission period for broadcast ofcontrol information from said intermediate apparatus to said destinationapparatus based on the determination.
 17. Non-transitorycomputer-readable media storing computer programs which, when executedon computing devices of a two-hop wireless time-division-duplexcommunication system, causes the system to carry out a transmissionmethod, the system comprising a source apparatus, destinationapparatuses and an intermediate apparatus, said source apparatus beingconfigured to transmit information along two links forming an indirectcommunication path extending from the source apparatus to at least oneof the destination apparatuses via the intermediate apparatus, and theintermediate apparatus being configured to receive information from thesource apparatus and to transmit the received information to the atleast one destination apparatus, a time-frequency format for downlinkand uplink subframes used for transmission in the system in discretetransmission periods, each discrete transmission period being a singledownlink or a single uplink subframe with a plurality of transmissionzones within each transmission period, each zone occupying a differentpart of that period, and being assignable to said source or intermediateapparatus for use in transmission, the method comprising: transmittinginformation along the relayed path as two successive transmissionsignals, link by link, said signals being transmitted using differentzones of a particular transmission period; wherein: a controlinformation zone in the particular transmission period is used forbroadcast of control information from said source apparatus to saidintermediate apparatus and said destination apparatuses; a first zone inthe particular transmission period is used for transmission from saidsource apparatus to said intermediate apparatus and a second, subsequentzone in the particular transmission period is used for transmission fromsaid intermediate apparatus to the at least one destination apparatus;said first and second transmission zones of the transmission period areeither side in time of a third transmission zone of the transmissionperiod, which is used for transmission along a single link forming adirect communication path from said source apparatus to anotherdestination apparatus, and in which there is no transmission orreception by the intermediate apparatus, but processing is performed insaid intermediate apparatus, so as to configure the information fortransmission in the second transmission zone based upon the informationreceived in the first transmission zone; said second zone is also usedfor direct transmission along a single link forming a directcommunication path from said source apparatus to a further destinationapparatus on the downlink, and said control information enables saidintermediate apparatus and said destination apparatuses to receivetransmissions in said first zone and said second zone, the methodfurther comprising: employing said first transmission zone to transmitinformation from the source apparatus to a still further destinationapparatus along a single link forming a direct communication path, sothat information is transmitted from the source apparatus to both saidintermediate apparatus and said still further destination apparatusduring the part of the particular transmission period corresponding tothe first transmission zone; determining whether the destinationapparatuses can receive the control information from the sourceapparatus and adding an extra control information zone in the particulartransmission period for broadcast of control information from saidintermediate apparatus to said destination apparatus based on thedetermination.
 18. An intermediate apparatus for use in a two-hopwireless time-division-duplex communication system, the system furthercomprising a source apparatus, and destination apparatuses, said sourceapparatus being configured to transmit information along a series oflinks forming an indirect communication path extending from the sourceapparatus to at least one of the destination apparatuses via theintermediate apparatus, and the intermediate apparatus being configuredto receive information from a previous apparatus along the path and totransmit the received information to a subsequent apparatus along thepath, the system using a time-frequency format for downlink and uplinksubframes for transmission in the system in discrete transmissionperiods, each discrete transmission period being a single downlink or asingle uplink subframe with a plurality of transmission zones withineach transmission period, each zone occupying a different part of thatperiod and being assignable to said source or intermediate apparatus foruse in transmission; and the intermediate apparatus comprising: atransmitter configured to employ said format for one transmission periodto receive information in a first zone window of said period and totransmit said information in a second, subsequent transmission zoneduring the same transmission period such that said information passesalong the two links in a single transmission period; wherein a controlinformation zone in the particular transmission period is used forbroadcast of control information from said source apparatus to saidintermediate apparatus and said destination apparatuses; said first zonein the particular transmission period is used for transmission from saidsource apparatus to said intermediate apparatus and said second,subsequent zone in the particular transmission period is used fortransmission from said intermediate apparatus to the at least onedestination apparatus; said first and second transmission zones of thetransmission period are either side in time of a third transmission zoneof the transmission period, which is used for transmission along asingle link forming a direct communication path from said sourceapparatus to another destination apparatus, and in which there is notransmission or reception by the intermediate apparatus, but processingis performed in said intermediate apparatus, so as to configure theinformation for transmission in the second transmission zone based uponthe information received in the first transmission zone; said secondzone is also used for direct transmission along a single link forming adirect communication path from said source apparatus to a furtherdestination apparatus on the downlink; said control information enablessaid intermediate apparatus and said destination apparatuses to receivetransmissions in said first zone and said second zone; and said firsttransmission zone is used to transmit information from the sourceapparatus to a still further destination apparatus along a single linkforming a direct communication path, so that information is transmittedfrom the source apparatus to both said intermediate apparatus and saidstill further destination apparatus during the part of the particulartransmission period corresponding to the first transmission zone;wherein the system further comprises a processor that determines whetherthe destination apparatuses can receive the control information from thesource apparatus and adding an extra control information zone in theparticular transmission period for broadcast of control information fromsaid intermediate apparatus to said destination apparatus based on thedetermination.
 19. A transmission method for use in an intermediateapparatus of a two-hop wireless time-division-duplex communicationsystem, the system further comprising a source apparatus and destinationapparatuses, said source apparatus being configured to transmitinformation along two links forming an indirect communication pathextending from the source apparatus to at least one of the destinationapparatuses via the intermediate apparatus, and the intermediateapparatus being configured to receive information from the sourceapparatus and to transmit the received information to the at least onedestination apparatus, the intermediate apparatus having access to atime-frequency format for downlink and uplink subframes used fortransmission in the system in discrete transmission periods, eachdiscrete transmission period being a single downlink or a single uplinksubframe with a plurality of transmission zones within each transmissionperiod, each zone occupying a different part of that period, and beingassignable to said source or intermediate apparatus for use intransmission, the method comprising: employing said format for one suchtransmission period to receive information in a first zone of saidinterval and to transmit said information in a second zone during thesame transmission period such that said information passes along the twolinks in a single transmission period; wherein a control informationzone in the particular transmission period is used for broadcast ofcontrol information from said source apparatus to said intermediateapparatus and said destination apparatuses; the first zone in theparticular transmission period is used for transmission from said sourceapparatus to said intermediate apparatus and the second, subsequent zonein the particular transmission period is used for transmission from saidintermediate apparatus to said destination apparatus; said first andsecond transmission zones of the transmission period are either side intime of a third transmission zone of the transmission period, which isused for transmission along a single link forming a direct communicationpath from said source apparatus to another destination apparatus, and inwhich there is no transmission or reception by the intermediateapparatus, but processing is performed in said intermediate apparatus,so as to configure the information for transmission in the secondtransmission zone based upon the information received in the firsttransmission zone; said second zone is also used for direct transmissionalong a single link forming a direct communication path from said sourceapparatus to a further destination apparatus on the downlink, and saidcontrol information enables said intermediate apparatus and saiddestination apparatuses to receive transmissions in said first zone andsaid second zone, the method further comprising: employing said firsttransmission zone to transmit information from the source apparatus to astill further destination apparatus along a single link forming a directcommunication path, so that information is transmitted from the sourceapparatus to both said intermediate apparatus and said still furtherdestination apparatus during the part of the particular transmissionperiod corresponding to the first transmission zone; determining whetherthe destination apparatuses can receive the control information from thesource apparatus and adding an extra control information zone in theparticular transmission period for broadcast of control information fromsaid intermediate apparatus to said destination apparatus based on thedetermination.
 20. A non-transitory computer-readable media storing acomputer program, which when executed on a computing device of anintermediate apparatus in a two-hop wireless time-division-duplexcommunication system, causes the intermediate apparatus to carry out atransmission method, the system further comprising a source apparatusand destination apparatuses, said source apparatus being configured totransmit information along two links forming an indirect communicationpath extending from the source apparatus to at least one of thedestination apparatuses via the intermediate apparatus, and theintermediate apparatus being configured to receive information from thesource apparatus and to transmit the received information to the atleast one destination apparatus, the intermediate apparatus havingaccess to a time-frequency format for downlink and uplink subframes usedfor transmission in the system in discrete transmission periods, eachdiscrete transmission period being a single downlink or a single uplinksubframe with a plurality of transmission zones within each transmissionperiod, each zone occupying a different part of that period, and beingassignable to said source or intermediate apparatus for use intransmission, the method comprising: employing said format for one suchtransmission period to receive information in a first zone of saidinterval and to transmit said information in a second zone during thesame transmission period such that said information passes along the twolinks in a single transmission period; wherein a control informationzone in the particular transmission period is used for broadcast ofcontrol information from said source apparatus to said intermediateapparatus and said destination apparatuses; the first zone in theparticular transmission period is used for transmission from said sourceapparatus to said intermediate apparatus and the second, subsequent zonein the particular transmission period is used for transmission from saidintermediate apparatus to said destination apparatus; said first andsecond transmission zones of the transmission period are either side intime of a third transmission zone of the transmission period, which isused for transmission along a single link forming a direct communicationpath from said source apparatus to another destination apparatus, and inwhich there is no transmission or reception by the intermediateapparatus, but processing is performed in said intermediate apparatus,so as to configure the information for transmission in the secondtransmission zone based upon the information received in the firsttransmission zone; said second zone is also used for direct transmissionalong a single link forming a direct communication path from said sourceapparatus to a further destination apparatus on the downlink; and saidcontrol information enables said intermediate apparatus and saiddestination apparatuses to receive transmissions in said first zone andsaid second zone, the method further comprising: employing said firsttransmission zone to transmit information from the source apparatus to astill further destination apparatus along a single link forming a directcommunication path, so that information is transmitted from the sourceapparatus to both said intermediate apparatus and said still furtherdestination apparatus during the part of the particular transmissionperiod corresponding to the first transmission zone; determining whetherthe destination apparatuses can receive the control information from thesource apparatus and adding an extra control information zone in theparticular transmission period for broadcast of control information fromsaid intermediate apparatus to said destination apparatus based on thedetermination.
 21. A source apparatus in a two-hop wirelesstime-division-duplex communication system, the system comprising thesource apparatus, destination apparatuses and an intermediate apparatus,said source apparatus being configured to transmit information along twolinks forming an indirect communication path extending from the sourceapparatus to at least one of the destination apparatus via theintermediate apparatus, and the intermediate apparatus being configuredto receive information from the source apparatus and to transmit thereceived information to the at least one destination apparatus, atime-frequency format for the downlink and uplink subframes used fortransmission in the system in discrete transmission periods, eachdiscrete transmission period being a single downlink or a single uplinksubframe with a plurality of transmission zones within each transmissionperiod, each zone occupying a different part of that period, and beingassignable to said source or intermediate apparatus for use intransmission, the source apparatus comprising: a transmitter configuredto transmit information along the path as a first of two successivetransmission signals, in a first link, the first and anothertransmission signal being transmitted using different zones of aparticular transmission period; wherein: a control information zone inthe particular transmission period is used for broadcast of controlinformation from said source apparatus to said intermediate apparatusand said destination apparatuses; a first zone in the particulartransmission period is used for transmission from said source apparatusto said intermediate apparatus and a second, subsequent zone in theparticular transmission period is used for transmission from saidintermediate apparatus to the at least one destination apparatus; saidfirst and second transmission zones of the transmission period areeither side in time of a third transmission zone of the transmissionperiod, which is used for transmission along a single link forming adirect communication path from said source apparatus to anotherdestination apparatus, and in which there is no transmission orreception by the intermediate apparatus, but processing is performed insaid intermediate apparatus, so as to configure the information fortransmission in the second transmission zone based upon the informationreceived in the first transmission zone; said second zone is also usedfor direct transmission along a single link forming a directcommunication path from said source apparatus to a further destinationapparatus on the downlink; said control information enables saidintermediate apparatus and said destination apparatuses to receivetransmissions in said first zone and said second zone; and said firsttransmission zone is used to transmit information from the sourceapparatus to a still further destination apparatus along a single linkforming a direct communication path, so that information is transmittedfrom the source apparatus to both said intermediate apparatus and saidstill further destination apparatus during the part of the particulartransmission period corresponding to the first transmission zone;wherein the system further comprises a processor that determines whetherthe destination apparatuses can receive the control information from thesource apparatus and adding an extra control information zone in theparticular transmission period for broadcast of control information fromsaid intermediate apparatus to said destination apparatus based on thedetermination.
 22. A transmission method for use in a source apparatusof a two-hop time-division-duplex wireless communication system, thesystem comprising: the source apparatus, destination apparatuses and anintermediate apparatus, said source apparatus being configured totransmit information along two links forming an indirect communicationpath extending from the source apparatus to at least one of thedestination apparatuses via the intermediate apparatus, and theintermediate apparatus being configured to receive information from thesource apparatus and to transmit the received information to the atleast one destination apparatus; a time-frequency format for downlinkand uplink subframes used for transmission in the system in discretetransmission periods, each discrete transmission period being a singledownlink or a single uplink subframe with a plurality of transmissionzones within each transmission period, each zone occupying a differentpart of that period, and being assignable to said source or intermediateapparatus for use in transmission, the method comprising: employing saidformat to transmit information along the path as a first of twosuccessive transmission signals, in a first link, the first and anothertransmission signal being transmitted using different zones of aparticular transmission period; wherein: a control information zone inthe particular transmission period is used for broadcast of controlinformation from said source apparatus to said intermediate apparatusand said destination apparatuses; a first zone in the particulartransmission period is used for transmission from said source apparatusto said intermediate apparatus and a second, subsequent zone in theparticular transmission period is used for transmission from saidintermediate apparatus to the at least one destination apparatus; saidfirst and second transmission zones of the transmission period areeither side in time of a third transmission zone of the transmissionperiod, which is used for transmission along a single link forming adirect communication path from said source apparatus to anotherdestination apparatus, and in which there is no transmission orreception by the intermediate apparatus, but processing is performed insaid intermediate apparatus, so as to configure the information fortransmission in the second transmission zone based upon the informationreceived in the first transmission zone; said second zone is also usedfor direct transmission along a single link forming a directcommunication path from said source apparatus to a further destinationapparatus on the downlink; and said control information enables saidintermediate apparatus and said destination apparatuses to receivetransmissions in said first zone and said second zone; the methodfurther comprising: employing said first transmission zone to transmitinformation from the source apparatus to a still further destinationapparatus along a single link forming a direct communication path, sothat information is transmitted from the source apparatus to both saidintermediate apparatus and said still further destination apparatusduring the part of the particular transmission period corresponding tothe first transmission zone; determining whether the destinationapparatuses can receive the control information from the sourceapparatus and adding an extra control information zone in the particulartransmission period for broadcast of control information from saidintermediate apparatus to said destination apparatus based on thedetermination.
 23. A non-transitory computer-readable media storing acomputer program which when executed on a computing device of a sourceapparatus of a two hop time-division-duplex wireless communicationsystem causes the source apparatus to carry out a transmission method,the system comprising: the source apparatus, destination apparatuses andan intermediate apparatus, said source apparatus being configured totransmit information along two links forming an indirect communicationpath extending from the source apparatus to at least one of thedestination apparatuses via the intermediate apparatus, and theintermediate apparatus being configured to receive information from thesource apparatus and to transmit the received information to the atleast one destination apparatus; a time-frequency format for downlinkand uplink subframes used for transmission in the system in discretetransmission periods, each discrete transmission period being a singledownlink or a single uplink subframe with a plurality of transmissionzones within each transmission period, each zone occupying a differentpart of that period, and being assignable to said source or intermediateapparatus for use in transmission, the method comprising: employing saidformat to transmit information along the path as a first of twosuccessive transmission signals, in a first link, the first and anothertransmission signal being transmitted using different zones of aparticular transmission period; wherein: a control information zone inthe particular transmission period is used for broadcast of controlinformation from said source apparatus to said intermediate apparatusand said destination apparatuses; a first zone in the particulartransmission period is used for transmission from said source apparatusto said intermediate apparatus and a second, subsequent zone in theparticular transmission period is used for transmission from saidintermediate apparatus to the at least one destination apparatus; saidfirst and second transmission zones of the transmission period areeither side in time of a third transmission zone of the transmissionperiod, which is used for transmission along a single link forming adirect communication path from said source apparatus to anotherdestination apparatus, and in which there is no transmission orreception by the intermediate apparatus, but processing is performed insaid intermediate apparatus, so as to configure the information fortransmission in the second transmission zone based upon the informationreceived in the first transmission zone; said second zone is also usedfor direct transmission along a single link forming a directcommunication path from said source apparatus to a further destinationapparatus on the downlink; and said control information enables saidintermediate apparatus and said destination apparatuses to receivetransmissions in said first zone and said second zone; the methodfurther comprising: employing said first transmission zone to transmitinformation from the source apparatus to a still further destinationapparatus along a single link forming a direct communication path, sothat information is transmitted from the source apparatus to both saidintermediate apparatus and said still further destination apparatusduring the part of the particular transmission period corresponding tothe first transmission zone; determining whether the destinationapparatuses can receive the control information from the sourceapparatus and adding an extra control information zone in the particulartransmission period for broadcast of control information from saidintermediate apparatus to said destination apparatus based on thedetermination.